Supporting Information Trapping Lithium into Hollow Silica Microspheres with a Carbon Nanotube Core for Dendrite-Free Lithium Metal Anodes Tong-Tong Zuo,, Ya-Xia Yin,, Shu-Hua Wang, Peng-Fei Wang,, Xinan Yang, Jian Liu,, Chun-Peng Yang and Yu-Guo Guo *,, CAS Key Laboratory of Molecular Nanostructure and Nanotechnology, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences (CAS), Beijing 100190, P. R. China University of Chinese Academy of Sciences, Beijing 100049, P. R. China Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences (CAS), Beijing 100190, P.R. China *Correspondence to: ygguo@iccas.ac.cn S-1
Experimental Section: Preparation of H-SiO 2 /CNTs: All the reagents used in the experiment were of analytical grade purity and were used as received. Multi-walled CNTs were first refluxed in 6 M HNO 3 solutions for 48h to remove the impurities and make them more dispersible in water. For a typical synthesis, 70 mg of the pretreated CNTs was ultrasonically dispersed into 140 ml distilled water to form a homogeneous suspension. 7 ml styrene monomer was added into 50 ml NaOH solutions (2 M) to remove the polymerization inhibitor and then extracted with water for 3 times. The styrene monomer after purification and 10 ml ammonium peroxydisulfate solution (0.04M) were transferred into the suspension. The suspension was then stirred under N 2 atmosphere at 70 ºC for 20 h to obtain the PS/CNTs. 200 mg PS/CNTs was ultrasonically dispersed into 150 ml distilled water containing 800 mg CTAB, 10 ml alcohol and 2 ml ammonia hydroxide (~28%). The solution with 1 g TEOs and 20 ml alcohol was slowly dropped into the suspension. The mixture was stirred for 10 h, followed by calcination at 600 ºC for 6 h under inert atmosphere. Structure characterization: Ultraviolet-visible spectroscopy was conducted on UV-2600 (Shimadzu, Japan) to test the physical property of the PS/CNTs. To characterize the silica coating layer, X-ray powder diffraction (XRD) analysis was performed with Rigaku D/max-2500 with Cu Kα radiation (λ=1.5405 Å) operated at 40 kv and 200 ma. Raman measurement was carried out from Thermo Scientific with a laser wavelength of 532nm. The nitrogen absorption and desorption isotherms were tested at 77.3 K from Quantachrome Instruments to evaluate the pore structure of the materials. X-ray photoelectron spectroscopic (XPS) was conducted on the ESCALab250 Xi (Thermo Scientific) using 200 W monochromatized Al Kα radiation to analyze the chemical composition on the electrode. To test the CNTs content of the materials, the thermogravimetric analysis (TG/DTA 6300) was carried out from 30 to 1000 ºC at 5 ºC min 1 under air atmosphere. SEM (6701F), TEM S-2
(2100F), HRTEM (2100F) and EDX elemental mapping (2100F) were employed to observe the morphologies, structures, sizes and elemental distribution of the materials. Electron energy loss spectroscopy (EELS) analysis was performed in STEM mode using the field-emission TEM (ARM200) equipped with a Gatan GIF Quantum965 spectrometer. Electrochemical characterization: To prepare the electrodes, H-SiO 2 /CNTs powders, carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) was mixed with the mass ratio of 8:1:1. The mixture was stirred in distilled water to form a homogenous slurry. After casting the homogenous slurry onto a Cu foil with a doctor blade, the H-SiO 2 /CNTs electrode was dried in vacuum oven overnight. The control sample of the H-SiO 2 -CNTs electrode was also prepared according to the similar procedure, excepting the mass ratio of H-SiO 2, CNTs, CMC and SBR is 7.2:0.8:1:1. The coin cells were assembled with Li foils, Celgard separators, electrolyte (1 M LiTFSI dissolved in DOL/DME, 50 µl) and the prepared electrodes. For the electrochemical cycling performance, the coin cells were tested with a capacity of 2 ma h cm 2 under the current density of 0.2, 0.5 and 1 ma cm 2. The Coulombic efficiency was calculated based on discharge and charge capacity to evaluate the Li-utilization during repeating plating/stripping processes. To assemble the full cell, Li anodes with H-SiO 2 /CNTs electrodes were first prepared with electrochemical plating method. LiFePO 4 cathodes were applied to pair with the plated Li anode. Full cells were tested at a rate of 0.5 C. S-3
Figure S1. UV-Vis spectra of CNTs, PS/CNTs and PS powders. S-4
Figure S2. Raman spectra of H-SiO 2 /CNTs, CNTs and SiO 2 powders. S-5
Figure S3. TEM images of H-SiO 2 microspheres (a) after Li deposition and (b) after electron beam irradiation. S-6
Figure S4. SEM image of bare Cu electrode after plating 2 ma h cm -2 of Li under the current density of 0.2 ma cm -2. The inset shows the optical image of the Cu electrode after Li deposition. S-7
Figure S5. TG curve of H-SiO 2 /CNTs before and after calcination. TG measurement was conducted under air atmosphere. The weight loss around 200 and 350 ºC correspond to the oxidation processes of residue organic compounds and PS, respectively. CNTs start to lose wight around 600 ºC. S-8
Figure S6. Cross-sectional view SEM images of H-SiO 2 -CNTs electrodes (a) before and (b) after plating 2 mah cm 2 of Li. Cross-sectional view SEM images of H-SiO 2 /CNTs electrodes (c) before and (d) after plating 2 mah cm 2 of Li. Scale bars. 50 µm. S-9
Figure S7. Top view SEM image of H-SiO 2 /CNTs electrode before plating. S-10
Figure S8. SEM image of H-SiO 2 /CNTs electrode after 10 cycles. S-11
Figure S9. Cross-sectional view SEM image of H-SiO 2 /CNTs electrode after plating 6 mah cm 2 of Li. Scale bar, 50 µm. S-12
Figure S10. XPS spectra of SEI components on different electrodes. The signals in (a-c), (d-f) and (g-i) were collected from the cycled H-SiO 2 /CNTs, H-SiO 2 -CNTs and bare Cu electrodes, respectively. S-13
Figure S11. Li metal nucleation overpential profiles of bare Cu, H-SiO 2 -CNTs and H-SiO 2 /CNTs electrodes. The nucleation overpentials are marked with two-way arrows. S-14
Figure S12. EIS Nyquist plots of different electrodes in Li symmetric cell after 1 and 5 cycles. The charge transfer resistance of H-SiO 2 /CNTs electrode decreases after 5 cycles, indicating an improved charge transfer kinetic. S-15
Figure S13. Electrochemical plating/stripping performance of different electrodes at a current density of 1 ma cm 2 and an areal capacity of 2 mah cm 2. S-16
Figure S14. Cycling performance of the full cell assembled with LFP cathode and Li anode with H-SiO 2 /CNTs electrode. The areal capacities of cathode and anode are 0.71 and 2 mah cm 2, respectively. The measurement was tested at 0.5C. S-17